1. Technical Field
The present invention relates generally to underground fluid pumping systems and more particularly, to such pumps which are capable of activating in response to surrounding liquid levels.
2. Discussion
Increased monitoring of environmental quality has resulted in a substantial rise in the number of identified sites of contaminated ground water. Accompanying this trend has been an increased effort to clean up these sites. In response, there is a need for improved below ground pumping systems to assist in these clean up efforts.
Ideally, pumping systems used for these purposes will have a number of characteristics. Because of the large number of pumps required is it desired to minimize the cost of each pump and installation. Accordingly, such pumps should be relatively simple and inexpensive and should fit in a small diameter well due to the increased cost of drilling larger diameter wells. To minimize maintenance and repair costs, the pumps should have a minimum of moving parts and should have high reliability. Also, such pumps should be able to withstand corrosive fluid streams without failure.
Due to the possibility of exposure to explosive gases pneumatic pumps are preferred over electrical pumps for pumping waste products. However, many of the currently used pneumatic pumps have a number of drawbacks. For example, many pumps in current use require external controlling devices which use timers to activate the pump on a fixed schedule. However, the necessity of external controllers adds considerably to the cost and complexity of the overall pumping system. In addition, the use of a fixed time pumping schedule has disadvantages since it may not result in pumping at the most opportune time to obtain maximum production. For example, such a configuration would not sense variations in the flow rate of fluid into the pump and may result in too fast or too slow pump cycles.
There are pumps which avoid the necessity of external controllers by incorporating sensing means within the pump to detect when fluid has entered the pump to a desired level. Unfortunately, the prior pumps which are capable of self activation have not proved satisfactory in many applications. One problem has been with the mechanical actuating and sensing mechanism within the pumps. Generally, such pumps use a float which raises when the pump fills and lowers when the pump is empty. Actuating mechanisms which sense the movement of this float sometimes require considerable force to switch the pumps pneumatic valve on and off. This results in the necessity of a fairly large and heavy float which increases the overall size and cost of the pump system. In addition, the actuating mechanisms in prior pump systems are exposed to the pumped fluid which may be highly corrosive. Thus, pump systems which are suitable for use in pumping inert materials may fail prematurely when the actuating mechanism is exposed to a highly corrosive fluid such as maybe found in contaminated well sites such as landfills.
In addition to problems with the actuating mechanism, the pneumatic valve used to control the flow of compressed air into these pumps have often proved unreliable. Spool type valves incorporating sliding seals are generally used in prior pumps of this nature. The force necessary to move these sliding seals to actuate spool type valves are one source of excess actuation force requiring the above mentioned large and heavy floats. In addition, spool type valves result in high maintenance and repair costs due to their tendency to freeze or to leak. There are a number of causes of the difficulties with sliding seals. These include debris entering the seals from the source of compressed air; contamination of the seals from the liquid being pumped; (especially where highly corrosive waste products are pumped) loss of lubrication in the seals; and compression set of the elastomeric seals if they remain inactive for an extended period of time. In addition, some pumps employ valves which have a significant cross over point where air supply is partially open and exhaust is partially closed. At this point the pump will tend to use a large amount of compressed air in an effort to switch to fully open or fully closed. In some cases the pump may reach a steady state with the head pressure in the surrounding well and remain in a cross over, or all ports open, position.
Another difficulty with sliding seals results from their use to provide a detent action between the discharge and refill cycles of the valve. As the sliding seals (which generally comprise of o-rings) wear, the ability of the o-rings to provide a detent action will be lost. This will result in short and erratic pump cycles unless the o-rings are replaced. Thus, it would be desirable to provide an underground pumping which overcomes some or all of the above-mentioned difficulties.
Accordingly, it is an object of the present invention to provide a simple and inexpensive pumping system for installing in small diameter wells. It is a further object of the present invention to provide such a pumping system which is reliable, has few moving parts, and which provides automatic on/off level control to eliminate the need for external controllers.
It is an additional object of the present invention to provide a underground pumping system which uses a pneumatic valve that avoids the use of sliding seals and which is switched from between pumping to discharge cycles with a minimum of actuation force. It is a further object for the present invention to provide such a system having a reliable and durable detent between pump discharge and refill cycles. It is still a further object of the present invention to provide an underground pump system in which the pneumatic valve is substantially isolated from the corrosive waste fluid stream.